This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The project involves measurement of very high (beyond 0.8 [unreadable]) resolution diffraction data from crystals of macromolecules or supramolecules of biological interest and evaluation of their structures with very high accuracy. This initiative aims at identification of subtle structural features, normally not seen at lower than atomic resolution. These are, for example, deviations of molecular stereochemistry from the typical target libraries, densities corresponding to bonding electrons resulting from breakage of the spherical atom approximation, location of hydrogen atoms and hydrogen-bonding networks, etc. Results of these investigations are relevant for construction of advanced geometrical restraint libraries, to be used in analyses at lower resolution and in accurate modeling of various interactions between macromolecules and various large and small ligands.